HBV infection is a global public health concern. Worldwide, 240 million people are chronically infected with HBV (Lavanchy and Kane 2016). Infection with HBV causes acute and chronic hepatitis leading to liver cirrhosis and hepatocellular carcinoma (Kew M C 2010).
Current therapy for HBV infection is limited, suppressing only viraemia without completely eliminating the virus, mainly due to the persistence of cccDNA (Tang, Yau et al. 2014). Withdrawal of therapy results in a rebound for most of patients, which has suggested the presence of a viral remnant responsible for persistent infection (Abdelhamed, Kelley et al. 2002). In patients undergoing antiviral therapy who discontinue treatment, HBV can reactivate from cccDNA (Petersen J 2007). To monitor the persistence of cccDNA in the liver, repeated liver biopsies are required, which are hazardous, uncomfortable, and costly to the patient (Wu, Johnson et al. 2014, Zhong, Hu et al. 2014, Shi, Sun et al. 2015). As cccDNA can also be found in the blood, especially after liver damage, its detection in serum or plasma allows the efficacy of antiviral therapy and the extent of liver damage to be evaluated without resorting to liver biopsies (Wong, Yuen et al. 2004, Takkenberg, Zaaijer et al. 2009).
After HBV infection, viral DNA is transferred to the nucleus of infected hepatocytes where rcDNA is released into the host cytoplasm. The viral DNA is eventually transported into the nucleoplasm where it is converted to cccDNA. Disguised as a minichromosome, the presence of cccDNA in the host nucleus serves as a template for continued virion transcription of messenger RNA in the hepatocyte nucleoplasm (Levrero, Pollicino et al. 2009, Nassal 2015). Thus, persistence of cccDNA remains an obstacle in clearing HBV by conventional antiviral therapy in chronically infected people, who remain at risk of developing advanced liver disease. Interestingly, there is small percentage of patients who clear HBV S-antigen (HBVsAg) by conventional anti-viral therapy alone, indicating cccDNA can be eliminated (Tavis, J E et al. 2013). This “cured” population can be withdrawn from life-long antiviral therapy, which is costly and has unknown side effects, if their cccDNA levels can be measured. A sensitive and specific method for quantification of cccDNA levels from liver biopsy or body fluids is thus highly desired to identify this “cured” population.
Elimination of cccDNA is the ultimate goal of HBV drug development research in finding a cure for HBV infection. A sensitive and specific method for quantification of cccDNA is highly desirable.